Typically in light duty latching mechanisms, such as employed in storm doors, rotation of the door handle positively moves the latch tongue to its unlatching position permitting opening of the door. Locking is accomplished by movement of a bar or other component to prevent rotation of the handle. Faced with an immobile handle, a potential intruder may apply sufficient force to the handle to result in breakage of a component of the latching mechanism. If latching is achieved by disconnecting the inside and outside handles from the latch, the potential intruder may well be discouraged by the knowledge that in spite of the force applied to the handle, the locking component will not be overcome.
The usual storm door latching mechanism does not provide a "dead bolt function". As used herein "dead bolt function" is to be accorded its broad meaning that a locking component, which could be the latch, is positively prevented from being moved to a non-interfering position, and is not to be construed so narrowly as to require a bolt separate from the latch. In the typical storm door latching mechanism, the latch is spring biased to its latching position. Thus through the use of a tool or a stiff plastic card inserted against the latch between the door and the doorway frame, the biasing force could be overcome and the latch deflected or pushed to its non-interfering position.
A prior art storm door latching mechanism includes a handle which is disconnected from the latch when the mechanism is in its latching condition. This mechanism also includes a separate dead bolt which is thrown by the use of a driver discrete from the components associated with the latch. This mechanism is relatively expensive and employs many parts. Furthermore the user is required to take a further step to throw the dead bolt over and above the step required to lock the latch.
U.S. Pat. No. 1,057,898 to Thomoson shows a lock assembly in which rotation of a small knob causes cam surfaces to shift the bolt out of alignment with arms which are rotated upon turning of a large knob thereby locking the bolt. The lock can be unlocked using a key which is received in a key slot. When the key is rotated, the lug held on the shaft including the key slot, engages a curved bar of the bolt to cause retraction of the bolt.
U.S. Pat. No. 2,733,089 to Grevenooed illustrates a latch mechanism for screen doors including a spindle having a generally square cross section. The mechanism also includes a locking bar which is horizontally slidable and includes an aperture having an enlarged end. When the locking bar is positioned so that the enlarged end receives the spindle, the handles can be rotated; however, when the locking bar is moved so that the spindle is received in the smaller end of the opening, the bar prevents the handles from moving thereby locking the mechanism.
U.S. Pat. No. 4,099,756 to Kaooura shows first and second bolt driving units. The second unit includes a knob which when pushed causes a pin to force the end of a first driver torque bar out of the hollow shaft used to actuate the latch bolt.
U.S. Pat. No. 2,707,121 to Behnke is directed to a screen door latch including a latching slide with a dog for reception in a recess of the spindle to prevent rotation.